Add display of handle when using multiple accounts (#2697)

- Shown on the main toolbar (subtitle)
- Shown just above the "replying to" message (even if not replying)

app/src/main/java/com/keylesspalace/tusky/MainActivity.kt

@@ -834,6 +834,9 @@ class MainActivity : BottomSheetActivity(), ActionButtonActivity, HasAndroidInje
         header.clear()
         header.profiles = profiles
         header.setActiveProfile(accountManager.activeAccount!!.id)
+        binding.mainToolbar.subtitle = if (accountManager.accounts.size > 1) {
+            accountManager.activeAccount!!.fullName
+        } else null
     }
 
     override fun getActionButton() = binding.composeButton

app/src/main/java/com/keylesspalace/tusky/components/compose/ComposeActivity.kt

@@ -236,6 +236,17 @@ class ComposeActivity :
         val composeOptions: ComposeOptions? = intent.getParcelableExtra(COMPOSE_OPTIONS_EXTRA)
 
         viewModel.setup(composeOptions)
+
+        if (accountManager.accounts.size > 1) {
+            binding.composeUsernameView.text = getString(
+                R.string.compose_active_account_description,
+                activeAccount.fullName
+            )
+            binding.composeUsernameView.show()
+        } else {
+            binding.composeUsernameView.hide()
+        }
+
         setupReplyViews(composeOptions?.replyingStatusAuthor, composeOptions?.replyingStatusContent)
         val statusContent = composeOptions?.content
         if (!statusContent.isNullOrEmpty()) {